Exercise may take several forms including aerobic or cardiovascular training, strength training, flexibility training, and balance training. With particular regard to strength training, two common forms include free weights and exercise machines. In the case of weight training exercise machines, it is common for the machines to include a user interfacing portion such as a graspable bar or handle, a foot press, a leg pad, or other interface. The interface may be connected to a cable or series of cables that may pass through one or a series of pulleys and may be connected to one or more weight plates.
A common exercise machine may include a weight stack where each plate in the stack is adapted to slide along two guide rods. The cable in these machines may be attached to a selecting rod passing through the weight stack and having multiple holes adapted to align with holes in each of the plates in the stack. A selection pin may be inserted into one of these multiple holes via a hole in a respective weight plate thereby engaging the selected plate, and all of the plates above it, with the selecting rod. As such, when the user manipulates the user interfacing portion, the cable pulls on the selecting rod causing the selected weights of the weight stack to be lifted along the two guide rods. Accordingly, a user may repetitively lift the selected weights to develop the muscular fatigue common in weight training.